The purpose of the screen and Semi-conductive layer on MV Cables

In most modern MV cables, especially underground, cables are shielded, or screened with an earthing conductor. The screen consists of lapped copper tape or metallic foil usually less than 1mm thickness which is the interface between the conductor and the insulation (PVC, XLPE). The main purpose of this conductive screen is to maintain a uniformly divergent electric field and contain the electric field within the cable core. The conductor screen is made from semi-conductive material which is designed to hold back voltage which smooths out the surface irregularities of the conductor by making the voltage on the inside of the insulation the same. This semi-conductive screen material is based on carbon black which is dispersed within a polymer matrix. The concentration of carbon black needs to be sufficient to ensure adequate and consistent conductivity. It must also be optimized to provide a smooth interface between the conducting and insulating components of the cable which is important as it decreases the occurrence of high stress regions on the cable. 

Semiconductive layer on MV Cables
Screen and Semi-conductive layer on MV Cables

The semi-conductive screen also reduces voltage stresses where the conductive components interface with the insulating components. It accomplishes this when the expansion of the insulating layer is typically 10 times greater than that of the conductor so that when the cable is at its maximum operating temperature of 90oC a large enough gap is formed to allow electrical discharges to occur. This then serves to even out the stresses associated with these discharges which would otherwise attack the insulation at specific points along the cable. 

The screen wires are connected at each extremity of the circuit in solidly grounded systems, dispersing the circulating currents of the MV cable. When connecting the screen wires, it is important to note whether the installation is using current transformers (CT’s) for the circuit protection. Any currents on the screen wires will be phasor summed in the conductor by the CT. In the case of fault currents, this is often directly out of phase with the conductor current. As the screen passes through the CT as part of the cable it is then necessary to bring the made-up screen wires back through the CT in the opposite direction prior to grounding. This ensures the screen current is effectively canceled out to ensure the correct operation of circuit protection devices.

How Power Factor Correction Can Save Your Business Money

Does your business spend to much money on electricity?

Power factor correction (PFC) is an often-overlooked component in large electrical installations. It measures how effectively your business uses power. With the majority of businesses within heavy industry having large power costs, todays article will show you how you can minimise these costs while increasing the efficiency of your electrical installation. 

How it works:

By assessing the ratio of real power (kW) to apparent power (kVA). Real power is the amount of power which is actually used by your onsite equipment (kW) whereas apparent power is the total amount of power (kVA) supplied to the site by the utility. A site with a lower power factor draws more apparent power than reactive power, thereby increasing your energy consumption usage. When you have a low power factor the voltage and current supplied becomes out of phase and requires correcting. Low power factor is generally caused by having large inductive loads on site (induction motors, air conditioning compressors, large lighting banks etc). The way in which this is corrected is by creating Reactive Power (kVAR) loads to your installation using capacitor load banks. This helps to correct the imbalance of voltage supplied and current drawn by equipment to become more in-phase with each other resulting in a better ratio of real power to apparent power. 

How Power Factor Correction Can Save Your Business Money 1

How it benefits your business:

  1. Reduced Demand Charges

If the power factor is low on your site, the percentage of the measured KVA will be significantly greater than the KW demand as mentioned above. Power factor correction will therefore lower the demand charge, helping to reduce your electricity bill.

  1. Increase in load capabilities of existing equipment

When circuits start drawing reactive power from an installed capacitor bank on site such as a PFC it causes a reduction in current flow from an improved power factor and may allow the circuits to carry new loads, saving the cost of upgrades when extra capacity is required. 

  1. Improved voltage

As the line current increases due to a low power factor the voltage drop in the conductor also increases which results in lower voltage supplied to equipment. PFC reduces this voltage drop in the conductor resulting in the correct voltages supplied to equipment. 

  1. Reduction in power losses

System conductor losses are proportional to the current squared (I2). Since the conductor current is reduced due to the power factor improvement, the losses are inversely proportional to the square of the power factor. 

  1. Reduced carbon footprint

By reducing your systems current power demand through PFC, your company puts less strain on the supply grid. Over time this lower demand can account for hundreds of tons of reduced carbon production by utilities. 

If you are looking to increase your power efficiency and cost and have not  yet considered power factor correction on your site, please give us a call for a free assessment and action plan. 

Author: Sam Soady







Why Effective Electrical Maintenance Can Save you Money

Unexpected downtime can be an expensive. When an electrical fault occurs, it occurs rapidly, often resulting in major damage to electrical assets. This leaves your business inoperable and vulnerable to the costs associated with downtime and loss of production.  By integrating an effective electrical maintenance program, you can ensure unexpected downtime does not happen. In this article you will understand how that translates into valuable cost savings for your business. 

What is Electrical Maintenance?

It is important to note that the above must be completed by a licensed electrician. 

Why electrical maintenance is important?

How electrical maintenance saves you money

Now that you are aware of the what, why and how of electrical maintenance it is important you speak to a qualified and licenced electrician about your specific electrical installation and what your site requires to operate safely and cost efficiently. For more information it is important to check the QLD Government website . We are the experts in electrical maintenance and can help you figure out the best program for your business needs. If you want to find out more please visit our website

Sam Soady

#electrician #electrical #electricalmaintenance #highvoltage #electricalengineering


How to Protect HV Underground Cables

Underground high voltage cables are a great innovation to the electrical distribution industry. While they make an installation look more visually pleasing than the overhead systems currently being utilized, they are often exposed to scenarios which are overlooked by electrical designers and engineers. It is common practice to protect your cables from mechanical damage via installation methods and manufacturing mechanical protection systems, however in some areas, cables have an environmental issue leading to a shortened lifespan and failure. Termites! Even though electrical cables are not considered food for the termites it is well known they can attack underground cables damaging the integrity of the installation, which eventually leads to failures. Some areas in Australia have a higher risk of termites such as the northern part of Queensland and the Northern Territory requiring underground cables to have an added protective layer during manufacturing. 

Methods for termite protection on underground systems include hard physical barriers such as:

  1. Rigid HD PVC Conduit systems.
  2. Added layer of plastic Nylon sheath (must maintain a smooth surface).
  3. Metal barriers such as brass, copper or steel tapes
  4. Chemical infused High Density Polyethylene with Cypermethrin

While all systems are highly effective at providing termite protection the most common method utilized for modern installations is the chemical infused High Density Polyethylene. This solution provides the most cost-effective solution as additional layers are not required to be added to the normal specification/design of the cable. Some companies however have moved away from this method due to Health and Safety concerns which has arisen from the use of these chemicals. 

When performing joints/terminations on the cable it is imperative to continue the termite protection all the way through the joint. This is generally achieved using stainless-steel mesh being installed as a protective layer over the joined cable (refer image). The use of roll springs or hose clamps ensures termites cannot enter the joint body.

How Power Factor Correction Can Save Your Business Money 2
How Power Factor Correction Can Save Your Business Money 3

Are you planning on installing underground cables on your electrical systems? Call us today to find out if you require extra protection for your cables.  

3 Key Components to Effective Electrical Maintenance

Unscheduled downtime can be very costly to your business. If you fail to schedule maintenance for your electrical assets, they will schedule it for you, usually in the most inconvenient way possible.

Our electrical maintenance programs can help you stay ahead of the game by implementing 3 key components that will ensure your electrical system is safe, reliable and effective. After reading this article you will understand how these components work together in assisting you achieve your electrical maintenance goals. 

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Thermography analyses heat signatures present in your electrical equipment to detect electrical faults before they progress to failures, without interrupting regular business operation. This gives our clients the opportunity to rectify faults before costly equipment damage occurs. Thermography has proven to significantly reduce unplanned downtime, reduce the risk of electrical fires, and save you money on costly repairs if the equipment were to reach the point of failure. 

Energised Maintenance:

Energised maintenance provides our clients with the opportunity to obtain live electrical data from their sites. Our highly skilled technicians can analyse this data to determine the health of their electrical system as a whole. This kind of testing allows us to increase the accuracy of a fault diagnosis within your equipment and identify any power quality issues you may be having on site. The data obtained gives us the opportunity to install equipment that can improve power quality, significantly decreasing power consumption and costs. 

De-energised Maintenance:

De-energised maintenance allows for planned shutdowns instead of unplanned outages. Equipment can be safely removed from service and visually inspected. The benefits include adjusting mechanical components and visual inspection that thermography and energised maintenance do not cover. Most mechanical faults are detected during de-energised maintenance which has saved our clients major headaches with the cost of downtime. 

Integrating these three components in your electrical maintenance program can severely diminish unfavourable outcomes on your site. For more information feel free to visit our website 

Sam Soady

#electrician #electrical #electricalmaintenance #highvoltage #electricalengineering 

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